For many HTC Desire user said, the haven’t received any confirmation via OTA update about Android Froyo (2.2). To make it sure you has OTA update or not for your desire try this method. First turn off your HTC Desire then go to Settings > About phone > System software update and force click Check Now, if you still can’t get OTA update try hits it for two times again. If you still didn’t get any updates try to check it using Wi-Fi connection and test it again. If you still didn’t get it, you unlucky about your HTC Desire.

HTC Desire - Froyo OTA Update

There are several reason why your HTC Desire didn’t get any update.

OTA Updates not yet available on your territory (You’ll need waiting)

Your Data Network not yet setup, so you can Check the updates

Don’t worry and be sad if you still didn’t get any update, try to rooted your HTC Desire and installed ROMS alternative. XDA-Developers. This is some of them

Froyo Sense LeeDROID Mod v1.6 (FRF91)
Based off HTC Froyo Sense 2.06 FR91 this one is fast, clean and stable and comes with lots of extra goodies such as the new Superuser permissions app by ChainsDD, custom boot screen, HTC Notes Widget, Desk Clock and Google Car Home. Known issues with this ROM are that there are no HTC Wallpapers. Latest update was 26-JUL-10. This ROMS created by by XDA member LeeDROID

Froyo AOSP OpenDesire v2.3a
This is Made purely for the HTC Desire, OpenDesire is compiled from the most recent AOSP source code available — it is not a port of any HTC ROM. Built with stability and reliability in mind, so unlike the ROM above, this one does not contain any additional applications. Latest update was 25-JUL-10, this ROMS created by by XDA member AdamG

If you still not suitable with this ROMS try to browse another HTC Desires ROMS available on this forum